Look at the size of the pots you win vs the size of the ones you loose. If your winning pots are all small compared to the pots you loose, then you should consider quitting that game, or change your strategy, if you can afford to. If not, quit.
To expand on this, what that means is that the other players, or at least most of them, can read you and cut their losses while maximizing their winnings. This goes back to "tells." Which I really don't pay a lot of attention to. Why? Because the really good players don't give any, and they also can give false tells. And since I don't play tournaments or No Limit, my exposure in any hand is equal to the bet and what the maximum number of raises is.
Notice I differentiated between "reading" and "tells." Reading is the ability to understand how the other person plays. Tells is information about "that particular" hand. And yes, reading does aid in tells. When I say, how the other player plays I mean is he loose or tight? Is he knowledgeable or dumb? Is he greedy? Does he call every time? Is he aggressive or passive? If a tight player makes an early raise I am apt to fold unless I can raise. If a loose player makes an early raise I am apt to just call or fold because the loose player plays so many hands you never are sure where he's at.
Now the previous is more complex than what I have written, but it should give you a start on the subject.
One of the things that I also get a kick out of is listening to the tournament announcers go on about "odds." Simply put, odds are based on what a result will be based on the number of cards available and the number of cards that can make a certain hand. I.e. if you have a pair before the flop the odds of flopping three of a kind (a set) is about 9 to 1. That is it will happen one time out of 10. Right? Wrong. Odds are based on thousands of hands played. Think of it as 100 times out of a 1000, or more. Said another way, in the long run they will be correct. But remember that in the long run we will all be dead.
But they are helpful in knowing what to do. If you have a small pocket pair and have to call a bet and two raises it is likely that you will have to make three of a kind to win. And given that your opponents have bigger pairs or bigger cards to make bigger pairs with, you may want to consider throwing that 33 in the muck unless the pot is big enough to make it worth your while.
Enough on card odds. There are many places on the Internet that will give you the various odds. Learn'em.